This invention relates generally to internal combustion engine pistons and, more particularly, to a connecting rod pin bearing for the piston in a four-stroke diesel engine.
Conventional bearing assemblies for crosshead pistons in four-stroke diesel engines are press-fitted into place and must be machined out for replacement when worn. This is a costly and time-consuming procedure which requires complete disassembly.
In recognition of the desirability of simplifying bearing installation, removal and replacement, several attempts have been made to develop an easily-replaced bearing assembly. These attempts have been based on two-stroke diesel connecting rod pin bearing technology. In two-stroke pistons, an insert bearing slipper is inserted within a recess formed in the wall of the piston head side of the pin bore. In a two-stroke application, opposed bearings are not needed, since reverse (upward) loading of the piston (and, thus loading of the bottom of the pin bore) is of negligible magnitude and seldom encountered.
Four-stroke engines pose a different situation in which substantial loads may be imposed between the underside of the pin and the bottom wall of the pin bore. Thus, bearings are needed on both the top and bottom of the pin. To maximize the effectiveness of these bearings, it has been found desirable to maintain close tolerances to minimize shock loading incurred by reciprocation.
U.S. Pat. No. 4,644,853 issued to Russell et al (Feb. 24, 1987), discloses a three-piece insertable bearing assembly for use in a crosshead piston. Based on two-stroke bearing technology, this patent provides an upper slipper bearing segment of less than semicylindrical arcuate extent which is slid axially into a broached recess in the upper portion of the pin bore. The slipper terminates in coplanar surfaces that engage the upper shoulders of lands formed in the sides of the pin bore. These lands serve to locate the slipper and prevent rotation of it during operation.
A pair of short lower bearing segments, or ears, are provided for axial insertion into similar less-than-semicylindrical recesses broached in the spaced portions of the piston skirt flanking the connecting rod operating area. These ear bearings also terminate in coplanar surfaces that engage the lower shoulders of the bore lands to prevent rotation during operation. Retaining rings are utilized on the axially inward sides of the bearing ears to prevent axially-inward movement of the ears into contact with the connecting rod during operation.
The bearing assembly disclosed in the Russell patent, following the two-stroke technology, has a true circular pin opening defined by the inner surfaces of the bearing slipper and ears and the pin bore lands, with close tolerances maintaining minimum clearance between pin and bearing. The three bearing segments are inserted axially into recesses broached into the pin bore. The lower ear segments are inserted into engagement with retaining rings. The lands have coplanar shoulders which are engaged by mating end surfaces of the bearing slipper and ears to prevent rotation of the bearing parts during operation. Axially-inward movement of the ears into contact with the connecting rod is prevented by retaining rings.
It has since been determined that bearing performance can be improved by providing a pin receiving bore that is not truly circular. Load-receiving arcuate portions of the slipper and ears are formed on arcs that have vertically spaced centers, creating a vertically elongated pin bore similar to an elliptical bore. In this arrangement, close tolerances are held at the sides of the pin/bearing interface, while the vertical separation of the arcuate load-bearing surfaces creates sufficient clearance for maintenance of an adequate oil film.
It is desirable to utilize this new technology in developing a commercially-feasible bearing design. It is therefore an object of this invention to provide a bearing assembly for a connecting rod pin in a piston that enables quick, economical installation, removal and replacement.